1. Field of the Invention
The present invention relates to downhole percussion drills in oil, gas, geothermal, and hot spring drilling, etc.
2. Description of the Related Art
The conventional rotary drilling has been widely used for the drilling of oil, gas, geothermal, and hot spring wells, etc. In this method, rock formations are crushed or cut by both of the rotation of a drill bit and the thrust on it.
It has been well known that rates of penetration and wellbore deviation problems can be greatly improved by giving impact blows to the drill bit. However, downhole percussion drills, which generate impact blows, have seldom been applied to deep well drilling, since they have problems as described below.
Air percussion drills for downhole use have been put to practical use in the fields for long time. They use compressed air to reciprocate the hammer to strike the bit and to remove cuttings from the bottomhole to the surface. However, they are not suitable when large influxes of water are encountered, since water invades into the tool and it causes insufficient bottomhole cleaning. Thus, the application of them to the fields has been limited to dry formations.
In order to solve these issues, downhole percussion drills operated by drilling fluids such as mud and water (called mud-driven downhole hammers, simply mud hammers) have been developed and tested worldwide (refer to the Japanese Utility Model Laid-Open No. 55-21352).
Mud hammers, in which the drilling fluid (mud or water) reciprocates the hammer to strike the bit, do not have the limitations of air percussion drills. However, they have several problems; for example, the sticking and cavitation of sliding parts, rapid wear of parts, and the clogging of fluid passages, since the drilling fluid itself has low lubricating ability and it contains abrasive fine rock particles. Although it is well recognized that percussion drilling has several advantages over conventional rotary drilling, we cannot find practical percussion drills that could be applied to the fields under various conditions at present.
The object of this invention is to offer downhole percussion drills with high reliability and durability, which could be used at various field conditions.
To solve issues mentioned above, a new type of downhole percussion drill was invented, which consists of a hammering mechanism driven by a hydraulic fluid (oil) with high lubricating ability, a hydraulic pump that pressurizes the hydraulic fluid, and a drive unit to operate the hydraulic pump. As the pure hydraulic fluid with high lubricating ability drives the hammering mechanism of this tool instead of drilling mud or water, the sticking and cavitation of sliding parts, rapid wear of parts, and the clogging of fluid passages are minimized. Therefore, this downhole percussion drill provides greatly improved reliability and durability.
Because drilling fluids such as mud and water can be used for the removal of cuttings in the same manner of the mud hammers, the tools also do not have limitations of air percussion drills. If the drilling fluids, used to remove cuttings, were also utilized as a power source of the drive unit, no extra means for supplying power to the drive unit would be needed.